My question involves landlord-tenant law in the State of: Illinois

My husband and I have a lease on a house in Illinois. My husband accepted a law enforcement job offer that had a residency requirement that we must move elsewhere. We gave written 30 day notice to the landlord, who then contacted us multiple times during that month asking if we could be out earlier. On the last day as we were finishing up cleaning, she arrived and informed us that she intended to sell the property(she is also a real estate agent.) Not a word was mentioned about breaking our lease.

I called her a couple of weeks after we moved out asking about our security deposit. She said she hasn't looked at our lease yet, and then claimed to do so while she was on the phone. She said we owe for the rest of the lease(about 6 months). My point to her was that she did not disagree with our moving and in fact tried to get us to move out sooner. If I had known she would have tried this, I would have offered to place an ad in the newspaper and shown the place myself, but since she didn't disagree and in fact said she wanted to sell it, I figured(silly me) that everything was fine.

Questions are: Is residency requirement for a job a valid reason for breaking a lease? If the landlord did not disagree with our moving(giving 30 days written notice along with reason) and tried to hurry us out, does that not imply agreement with us leaving? If we are still liable for the balance of the lease, doesn't she have to attempt to rent/sell it?